1. Field of the Invention
The present invention relates to a broadband wireless communication system. More particularly, the present invention relates to a method and an apparatus for supporting a handover in a broadband wireless communication system.
2. Description of the Related Art
In the 4th Generation (4G) communication system, research for providing users with services having various Quality of Service (QoS) with a transmission rate of approximately 100 Mbps is in progress. In the current 4 G communication system, research for supporting high-speed services for a Broadband Wireless Access (BWA) communication system, such as a wireless local area communication network system and a wireless metropolitan area network system, in a form of securing mobility and QoS have been actively undertaken. A representative communication system is the Institute of Electrical and Electronics Engineers (IEEE) 802.16 system.
FIG. 1 is a view illustrating a macro cell in which a plurality of femto cells is installed in the IEEE 802.16 system according to the related art.
Referring to FIG. 1, the plurality of femto cells are included in a first macro cell C-10 formed by a first macro base station 10 and a second macro cell C-20 formed by a second macro base station 20.
When a terminal enters a coverage area of a neighboring base station from a serving base station from which the terminal is receiving the service, the terminal performs a handover in order to continuously receive the service. In this case, the terminal re-selects a new base station for entrance. According to a handover method in the IEEE 802.16e system, the terminal receives a neighbor base station list from the serving base station, searches for neighbor base stations by using the neighbor base station list, and then determines a handover target base station.
In order to support rapid handover, the first macro BS 10 registers the neighboring second macro BS 20 and other macro base stations in the neighbor list.
The first macro BS 10 inserts radio configuration information of respective adjacent base stations, as well as a list of the adjacent base stations, in the neighbor list. The first macro BS 10 inserts Base Station IDentifiers (BS-IDs) of the corresponding adjacent base stations in a MOBile_NEighBor-ADVertisement (MOB_NBR-ADV) broadcast message and transfers the neighbor list to terminals located within the cell.
Accordingly, the terminals may perform the rapid handover by periodically measuring signals of the neighbor base stations and using the measured signals. The terminal measures a Received Signal Strength Indicator (RSSI) and a Carrier to Interference and Noise Ratio (CINR) of each adjacent base station by using information, such as a center frequency, a bandwidth, an FFT size, a preamble index, a frame duration, and Base Station Equivalent Isotropically Radiated Power (BS_EIRP) of the adjacent base station obtained through the MOB_NBR-ADV received from the serving base station which the terminal currently accesses. The RSSI and the CINR of the adjacent base station are compared with an RSSI and a CINR of the serving base station, and one or more adjacent base stations are selected as handover target base stations by using the comparison result. Accordingly, a transmission power (TX power) of the base station included in the neighbor list is a necessary factor for the determination of a normal handover of the terminal. However, in the WiMAX standard, the number of neighbor lists available in one base station is limited to 255, and all base stations must use unique Base Station IDentifiers (BS-IDs). Accordingly, when a plurality of pico BSs or femto BSs are included in one macro BS area, it is impossible to provide a normal handover to the terminal due to the limitation of the number of neighbor lists. An alternative for overcoming the limitation of the number of BS-IDs includable in the neighbor list and performing a smooth handover is desired.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.